Applied Psychoacoustics Lecture 1: Anatomy and Physiology of the human auditory system

1. Applied PsychoacousticsLecture 1: Anatomy and Physiology of the human auditory system Jonas Braasch

2. Overview of the Human Ear

3. Outer Ear • Pinna: External cartiledge • Provides direction dependent frequency cues for sound localization through spectral filtering • Position can be actively controlled by some mammals (e.g., cat) • Meatus (Auditory Canal) • Pathway to the middle ear, approx. 7mm diameter, 27mm length • Amplifies sounds in the range of 2000 to 5000 Hz through resonance (approx. 10 – 15 dB)

4. Simulation of the sound pressure wave in the ear canal 1 2 3 1 frontal, 2.7 kHz 2 lateral, 10 kHz 3 rear, 2.7 kHz

5. Photo of ear drum

6. Middle Ear http://www.bioon.com/book/biology/whole/image/11/11-5.jpg

7. Middle Ear

8. Middle Ear • Tympanic Membrane • Sound pressure vibration is trancduced into mechanical oscillation and passed on to the malleus • protects ear (e.g, water, wind) • Ossicles • Malleus, incus, stapes (hammer, anvil, and stirrup) • are the Smallest bones in human body • Muscles • Stapedius muscle (connected to the stapes) • Tensor tympani muscle (connected to the malleus) • are the smallest muscles in the human body • Oval Window • connection to the cochlea • Eustachian Tube • connects the middle ear to the throat for pressure relief

9. Function of the middle Ear • Is an impedance transformer • Without it difference in densities of air and the cochlear liquid would result in lossy energy transfer • Pressure increase the pressure between the oval window and the ear drum by nearly a factor of 30 • Amplitude ratio ear (drum/stapes) ~1.3:1 • Area ratio (ear drum /oval window): ~20:1

10. Acoustic Reflex • Transmission can be attenuated in the middle ear by stiffening the Stapedius muscle and the tensor tympani muscle to protect the inner ear • Is controlled by the auditory system and react to loud sound exposure

11. Arrangement to measure the pressure-force transfer function of a middle ear (RUB-IKA)

12. Vibration of the ossicular chain

13. Vibration of the ossicular chain

14. Vibration of the ossicular chain

15. Inner Ear Semicircular canals Auditory Nerve Cochlear

16. Basilar Membrane

17. The Traveling Wave in the Basilar Membrane

18. Frequency Mapping on the BM Logarithmic Frequency Mapping http://www.bioon.com/book/biology/whole/image/11/11-10.jpg

20. Traveling Wave Simulation 250-Hz Tone 1000-Hz Tone 4000-Hz Tone http://www.boystownhospital.org/Research/Areas/Neurobiological/MoreInfoComLab/traveling_waves.asp

21. Neurotransmitters • are chemicals that enable communication between two neurons • are released from one neuron at its presynaptic nerve terminal and cross the synapse, a small gap, to the receptor of the second neuron

22. Connecting the ear to the auditory pathway • 95% of auditory nerve fibres (Type-I fibres: large diameter, myelinated) innervate IHCs (20- 30 to a single IHC) sending information to the CNS • 5% (Type-II fibres: thin, unmyelinated) innervate OHCs (each fibre innervating 50-100 OHCs)

23. Tonotopic organization of auditory nerve and cochlear nucleus

24. Definition Tonotopy (from greek tono- and topos = place: the place of tones) is the spatial arrangement of where sound is perceived, transmitted, or received. It refers to the fact that tones close to each other in terms of frequency are represented in topologically neighbouring neurons in the brain. from Wikipedia

25. Cell Response Types • Primary-like (PL) • Primary-like, notch (PL-N) • Phase-lock (onset) • Onset, lock (O-L) • Chopper

26. Cell types chopper Primary-like time time Acoustic stimulus Acoustic stimulus onset Primary-like, notch time time Acoustic stimulus Acoustic stimulus

27. Tuning Curves

28. Post Stimulus Time (PST) Histogram

29. Phase Locking action potential sound pressure

30. Physiological Coordinate System